Have you ever wondered whether running is useful for burning fat ? How about whether low intensity, long duration (ie. exercising in your fat burning zone) running (or cardio) is better than higher intensity interval running (ie. your cardio zone)?
Well, we’re about to answer those questions .
RUNNING TO BURN FAT
Depending on the duration and intensity of your run, your body will rely on carbohydrates (stored as glycogen in the muscles and liver) and fat for its fuel.
Your body chooses different fuels during different situations . Because fats yield more calories and are slower burning as they are metabolized, they tend to be used over longer durations when compared to carbohydrates.
Conserving blood glucose and glycogen stores are your body’s first priority . As you become fitter your body will become more efficient at using fats for fuel while sparing your vital carbohydrate reserves.
You will obiviously fatigue sooner if you are someone who is totally unfit , one of the reasons being that their carbohydrate stores are more quickly dissolved and utilized. Fitter individuals can run for much longer because they have developed the ability to use the slow burning fats as fuel, and therefore conserve their energy better.
As the intensity of exercise increases, there is more reliance on carbohydrates for fuel . Typically, intensities greater than 70% of VO2 max (or maximum heart rate for our purposes) will use carbohydrates as the dominant fuel source.
However, this doesn’t mean that working at high intensities doesn’t burn fat.
This is where most people get confused. Many people conceive that, for instance, since running at a lower intensity implies more reliance on fat as fuel, they feel the need to run at this low-intensity to burn fat! Nothing could be further from the truth!
A study in the New England Journal of Medicine demonstrated that, compared with a control group 8 months of either low amount/moderate intensity, low amount/high intensity or high amount/high intensity exercise all led to positive changes in overall lipoprotein (one type of blood fat) profile in overweight subjects. The latter group (high amount/high intensity) also gained the best training, fat loss, and blood lipid effect!
The other part of the fat burning question is that the longer you run (or exercise), the greater the reliance on fat as a fuel . Once again, this feeds the myth that running (or doing cardio) for long periods of time is essential to burn fat. I call this the “marathoner mentality”.
The first thing that is critical to understand is this :
A calorie is a calorie and 1 pound of fat is equivalent to 3500 calories.
Since burning fat ultimately boils down to creating a negative energy balance (ie. more calories expended than consumed) the goal is choose a method of running training that will elicit the maximum number of calories expended – not just during the activity but afterwards as well !
Working at higher intensities promotes a greater total calorie loss (even after you’re finished exercising) and that’s what really matters if you’re looking to lose weight and burn fat .
As we’ve already described, fat is the major contributor to muscle energy during low-intensity exercise . Therefore, most people intuitively believe that low intensity training must therefore induce an increased muscle fat burning effect (known as lipolytic activity).
The enzyme, HSL (hormone sensitive lipase), is required to catalyze the hydrolysis (breakdown) of stored triglycerides (fats) in skeletal muscle as it does in adipose (fat) tissue. Furthermore, several studies have indicated that HSL is probably the main lipase responsible for triglyceride hydrolysis during exercise.
However, a remarkable study investigating the effects of exercise of extreme duration at low-intensity on body fat profile had subjects complete a 32-day crossing of the Greenland ice cap on cross-country skis. After this incredible crossing, the researchers discovered that HSL activity was NOT influenced by the prolonged low-intensity physical activity in either arm or leg muscle. This is consistent with results from similar investigations .
Be my guest if you really have the time to run 2-3 hours at a low intensity . You will achieve some degree of fat loss but studies have shown that you will need to perform a enormous amount of exercise to gain the benefits you desire.
Furthermore, several studies have demonstrated that your aerobic endurance will either decline or remain unchanged by exercising at low intensities for long periods of time!
So why not save time, dramatically improve your aerobic fitness, and burn more fat by upping the intensity of your running workouts? The choice is yours!